1. Field of the Invention
The invention relates to bubble memories and in particular to the detection thereof.
2. Description of the Prior Art
A recognized shortcoming of present-day bubble memory devices has been that their error rate (i.e., errors per number of bits read during a cycle) is not equivalent to that of other known digital memory devices such as magnetic tape, drums and disks. The error rate criteria for tape, drums and disks is established at the present time as one error per 10.sup.9 bits of read data. As of this time, the error rate of bubble memories is several orders of magnitude under the above rate. Hence, it is clear that if the bubble memory is to become viable in today's commercial marketplace, it must improve its error rate.
The errors that may be generated by a bubble memory are designated as either soft or hard errors. Soft errors are defined as errors which arise because random or sporadic noise may be interpreted as a signal (i.e., presence of a bubble), whereas hard errors are errors produced by an unaccounted for disappearance of a bubble signal or bubble, either in the bubble's electronics or in its integrated circuitry. The present invention has as its purpose to minimize the soft errors.
Known prior art bubble detection techniques have encountered a relatively high soft error rate since the bubble signal is difficult to distinguish with respect to high background noise. The background noise is due primarily to a rotating magnetic field which is generated by a mechanism for propagating bubbles around its circuit loop. Now the prior art makes only one attempt to determine whether a bubble signal is present or not present in a certain time frame and it has been determined that the above-mentioned background noise sometimes is interpreted as a bubble signal whereas in reality there is no such signal present.
Accordingly, it is an object of the present invention to obviate the above-mentioned shortcomings of the prior art.